An IP address is a unique number that identifies a particular computer on the internet. The most common IP based system currently, which everyone can use, assigns four numbers from 0 to 255. These numbers were picked because they have a very nice set of binary representation, as binary is more important to computers. One part of the numbers represents the organization, like MIT, or the US government, or Xinhua news, and the second part represents the particular computer or server in the organization When the Internet was first developed, huge sections of these numbers were passed out to various organizations on the grounds that there could never POSSIBLY be that many sites on the Internet.

So many years later, we are running out. The few remaining grassy squares on the chart show what was left when Randall drew this comic and there are now even fewer than that. If you want a new website or Internet hosting company or ISP, then you need one of those squares. Pretty soon we'll be totally out and then there can be no new internet until we get everyone to use the new system.

Anticipating that this might be a new problem, a new system called IPv6 was developed in which the organization vs individual computer distinction doesn't really exist, and there are 20 numbers instead of four, which could identify pretty much every atom in the known universe with an address if we needed to. A lot of the internet doesn't support IPv6 yet, but pretty soon we will have to or there can never be any more sites or connecting computers. Ever.

Windows XP's default wallpaper was a picture of an empty grassy field. Almost no one outside of China is using IPv6 yet (China has to on the grounds that it has 1.3 billion people who all want to go online and was allocated almost no IPv4 addresses), but it has a preposterous number of addresses. So it'll be big and empty and the average address won't have anything, so feel free to take as many as you like.